Lubricant containing selenium compounds



Patented May 20, 1952 UNITED STATES LUBRICANT CONTAINING SELENIUM COMIPOUNDS Warren Lowe, William T. Stewart, and James 0. Clayton, Berkeley, Calif., assignors to California Research Corporation, San Francisco, Calif., a

corporation of Delaware No Drawing. Application July 9, 1949, Serial No. 103,937

9 Claims.

The present invention relates to lubricatin oils compoundedwith selenium-containing compounds, such as dialkyl selenides, which attack silver and like metals, thereby decreasing the effectiveness of the selenium compound in lubricating oils. In order to prevent the loss of effectiveness of the selenium compounds by attack on silver and like metals, certain protective agents such as 2mercapto-4,6,6-trimethylthiazine are added to the lubricating oils.

As is well known, the present-day problems involved in the lubrication of internal combustion engines are extremely complex and difficult to overcome due mainly to the great load imposed on the bearings, the high engine speeds, and. the elevated operating temperatures. To avoid rapid deterioration resulting from such severe operating conditions, lubricating oils have been compounded with various improving or stabilizing agents. Of the various lubricating oil compounding agents, a group of highly effective additives is the selenium-containing organic compounds. For example, aliphatic mono-, di-, and higher poly-selenides, seleno-mercaptans, metal selenomercaptides, etc. are highly effective oxidation inhibitors. Unfortunately, oils compounded with such selenium-containing compounds are adversely affected by silver and like metals. The deleterious action involves a direct attack of the metal by selenium, resulting in a rapid discoloration of the metal surface and formation of metal selenides and the subsequent sloughing ofi' of these metal selenides during engine operation. As the selenium of the selenium-containing compounds attacks the metals during engine operation, the effectiveness of the selenium compounds as addition agents in lubricating oils is considerably decreased. For example, when a selenium compound is added to a lubricating oil to inhibit oxidation, the effectiveness of the selenium com- 3 pound is considerably decreased as the seleniumcontaining compound attacks the metal. Also, when the selenium-containing compound attacks the metals in an engine, there is a substantial loss of bearing metal and a pitting of bearing surfaces.

Thus, it may readily be seen that when the selenium of a selenium-containing oxidation inhibitor attacks metals of bearing surfaces, etc., there is a two-fold loss to the system, namely, a reduction in the efiectivenss of the seleniumcontaining compound as an oxidation inhibitor and a loss of sensitive metal from the bearing surfaces during engine operation. It is apparent that in spite of the long desire to lubricate silver bearings with lubricants compounded with selenium compounds, it has been impractical to do so in view of the aforementioned diificulties.

Because of these difficulties with lubricants containing selenium compounds, there is a tendency to eliminate the highly eifective seleniumcontaining additives from the Diesel lubricating oils, thereby losing the remarkable benefits of theseadditives. For example, heretofore, it has been undesirable to use these effective selenium anti-oxidants in lubricants employed for engines containing silver bearings, such as in certain railroad Diesel engines containing silver wrist pin bushings. Alternative practices have been to eliminate the selenium-containing additives from the oil, allowing the oil to deteriorate more rapidly through oxidation; or include the selenium-containing additives, allowing the oil to,

deteoriate less rapidly through oxidation with a consequent selenium attack on the silver wrist pin bushings. Because of the presence of the silver in many aircraft engines, it has not been feasible to use the highly effective selenium-containing aviation oil additives.

Therefore, it is an object of this invention to provide a selenium compound-containing lubricant which is stable to sensitive metals such as silver, whereby the effectiveness of the selenium compounds as oxidation inhibitors is not reduced by the reaction of the selenium compounds with the sensitive metal surfaces.

In the attainment of these objects, the present invention concerns the combination of a lubricant compounded with selenium compounds, and a silver-protective agent which greatly minimizes attack on silver by the selenium compounds, whereby the essential functions of the selenium compounds are maintained at maximum activity.

Now, through the use of the silver-protective agents in accordance with the present invention, lubricating oils compounded with selenium-containing additives can be used in Diesel oils, aviation oils, and any other oils Where selenium attack on sensitive metals is a problem, to provide a stable lubricant having selenium compounds of increased effectiveness. While the outstanding advantages of the action of the silver protective agents in lubricants containing selenium compounds is particularly apparent in heavy-duty motor oils, the inventive combination finds application in turbine oils, gear oils, such as for use in hypoid gears, cutting oils, soluble oils,

greases, etc.

The silver protective agents include 2-thiothiazine compounds of which Z-mercapto-thiazine is the simplest member. Also included are the derivatives of said simplest member, wherein the mercapto-hydrogen may be replaced by a hydrolyzable group, and where there may be shortchain saturated and unsaturated aliphatic groups substituted on the ring carbon atoms. The shortferred that the thiazine ring contain not more than 4 substituents having a total of not more than 16 carbon atoms. It is preferred that each...

substituent group on the thiazineringcontainnot.

more than 4 carbon atoms. By short-chain 'ali-.:

phatic groups is meant aliphatic groups contain-- ing not more than 8 carbon atoms;

The hydrolyzable group is one which -may;react on hydrolysis to yield hydrogen in the-mercapto group, and includes cationic salt-forming atoms and radicals including metals (e. g., sodium,,.-po -1 tassium, barium, calcium, zinc, aluminum, etc); I

groups obtained by salt formation with amines (e. g., trimethylamine, n-butylamine, dodecylamine, ammonia, etc.) amide radicals (e. g., cy-

clohexylamide radical and organic carboxyl and. thionyl radicals such as 'benzoic anddiethyldie thiocarbonyl radicals) Examples of -2-thio-thiazine compounds are: .2-

mercapto-4,6,6-trimethyl thiazine; zinc. salt of. 2-" mercapto-4,6,6-trimethyl thiazine; Z-mercaptoe l,3-dihydrothiazine; 3-mercapto 2,4,1-thiazine; 2 mercapto4-methyl thiazine; 2 mercapto 4- ethyl thiazine; 2mercapto-4,6-dimethyl thiazine;

2 mercapto-i-isobutenyl-6,6-dimethyl thiazine;..

4,6,6 trimethyl thiazine 2 cyclohexyl sulfenamidej and the butyrate ester of 2-mercapto-thiazine. Examples of .1 2-thio-thiazine compounds also include the reaction products obtained by reactinga 2-mercapto-thiazine with the follow! ing: carboxylic acids,-alpha-beta unsaturated ketones, esters, olefins, nitriles, organometallic compounds, sulfonyl halides, ethylene oxide, anhydrides and acyl halides.

Because of the greater effectiveness obtained, it is preferred to use-2-mercapto-4,6,6-trimethyl thiazine to prevent selenium attack on silver.

The 2-thio-thiazines embraced in this invention vary in effectiveness-in minimizing the lossof the effectiveness of the selenium compounds; some of the 2-thio-thiazines,-for example, are: effective when used in amounts as low as 0.001 (by weight of total composition) Certain of the 2-thio-thiazines have only limited solubility in the lubricating oil and are effective at that solubility. All

on-silver and like metals may be obtainedby us-- ing 2-thio-thiazole compounds in conjunction with the Z-thiazine compounds.

Examples of 2-thio-thiazoles-are: Z-mercaptobenzothiazole, N-cyclohexyl '2-benzothiazyl sulfenamide; dodecyl aminesalt of mercaptobenzo thiazole; zinc salt of mercapto-benzothiazole; 2-

mercapto-S-methyl, thiazole; 2-mercapto-5-ethyl thiazole; Z-mercaptoi-methyl thiazole; etc:

Suitable baseoils include a wide variety of lubricating oils such as naphthenic base, paraflin base, and mixed base mineraloils, other hydro' carbon" lubricants, e. g., lubricating -oil derived from'coalproducts, and-synthetic oils, e. g., alkylg ene polymers '(such as polymers. of propylene,

butylene', etc;,' and mixtures thereof), alkylene oxide=type polymers; dicarboxylic acid GStBI'SIaIId liquid esters; of acids of phosphorus. Synthetic oils of. the alkyleneoxide-type polymer vwhich may be used include those exemplified by the al-' For example, it is preferred to The major kylene oxide polymers (e. g., propylene oxide polymers) and derivatives, including alkylene oxide polymers prepared by polymerizing alkylene oxides, e. g., propylene oxide, in the presence of wa- .;;ter:-or.alcohols, e. g., ethyl alcohol, and esters of 'alkylene oxide-type polymers, e. g., acetylated propyleneoxidepolymers prepared by acetylat- 'ing prop-yleheoxide polymers containing hydrox- Synthe'ticoils of. the dicarboxylic acid ester type include. those-which are prepared by esterifying such dicarboxylic acids as adipic acid, azelaic acid, suberic acid, sebacic acid, alkenyl succinic acid, fumaric acid, maleic acid, etc., with alcohols such as butyl alcohol, hexyl alcohol, 2-ethyl-hexyl alcohol; -,dode.cyl alcohol; etc. Examples of dicarbOXYliCifiCid ester synthetic oils include di-butyl adipate, di,hexyl adipate, di-Z-ethyl-hexylseb-.:

acate, ;di-:n -hexyl 'fumarate polymer, etc.

Syntheticioils. of thetypeof liquid esters-of. acidsi of phosphorus. include the esters, of l PhOS-r phoric: acid, 'e. g.,;tricresyl' phosphate ;r* the esters:

of ,phosphonic acid, :e.-g.,"di,-ethy1 ester, of decane phosphonic'sacid or'other suchestersas obtained by reacting alkyl phosphonyl chlorides withv hy-.

droxyl-containing' compounds such as phenols andaliphatic alcohols, and with olefin oxides such i as-propylene .oxide, as described in Jenseniet -al., U. S. patent application No. 86,856, new abanw doned.

The improved lubricant of the present .inven-.-. tionis used where the effectiveness of selenium: compounds as lubricant additives. is decreased by the attack on metals by the selenium of the"- .selenium compounds; In order to evaluate. the;

silver-protective agents of this invention for their effectiveness in inhibiting reduction of activity of. selenium compounds, lubricants containing the selenium compounds and the. protective agents were subjected to a silver strip test which was:

performed as follows:

A silvermetal strip having the dimensions .of

2 x x gg". was first cleaned with a wire brush until the strip was highly polished. The strip was weighed and the weight recorded. This highly polished silver strip was then placed in a 600 ml. beaker in such a manner that the strip was completely immersed when 300 g. of the oil being tested was poured into the beaker. The .oil

was stirred at a temperature of 300 F.'for twenty hours, at which time the silver strip'was removed and" cleaned, first with chloroform, then with The appearance of the strip was noted. 7 Those strips which had been severely attacked were quite black. The tested silver strip petroleum ether.

was washed in-a concentrated solution of cadmium chloride containing 10% of potassium cyanide to remove the selenide film adhering tothestrip; After the strip had been-washed with thiscadmium chloride-potassium cyanide solution and dried, it was weighed. The diiference in weight of the original strip and the strip after the cadmium chloride wash was noted and recorded asthe weight lost due to reaction with the selenium compound.

In addition to being especially eifectiveas pro-- tectiv'e agents for silver, the protective agents of this invention are eifective ,in protecting other selenium-sensitive metals from selenium attack.

Such other selenium sensitive metals includecopper, aluminum, and alloys of copper and aluminum.

The following are illustrative of various selenium-containing oxidation inhibitors reactive with silver: alkyl selenides (e. g., didodecyl monoselenide, octadecyl methyl monoselenide, octadecyl ethyl moncselenidaoctyl dodecyl monoselenide, di eic'osyl' monoselenide, dioctyl diselenide, di-eicosyl diselenide, dilauryl diselenide, dioctadecyl diselenide, and the various monoand polyselenides prepared by reacting sodiumor other alkali metal monoor polyselenides with halogenated, e. g., chlorinated hydrocarbons, such as decyl'chloride, dodecyl chloride, tetradecyl chloride, octadecyl chloride, heptadecyl chloride, chlorinated lubricating oil and chlorinated wax) selenomercaptans (e. g., methyl selenomercaptan, octyl selenomercaptan, dodecyl selenomercaptan, tetradecyl selenomercaptan, hexadecyl selenomercaptan, octadecyl selenomercaptan, eicosyl selenomercaptan, parafiin wax selenomercaptan, phenyl methyl selenomercaptan, phenyl octyl selenomercaptan, phenyl dodecyl selenomercaptan, phenyl octadecyl selenomercaptan, cyclohexyl selenomercaptan, octyl cyclohexyl selenomercaptan, octadecyl cyclohexyl selenomercaptan, etc); metal selenomercaptan (e. g., the barium, calcium, sodium, zinc, strontium, aluminum, cadmium, nickel, lead and thallium salts of the above selenomercaptans).

Some of the above-indicated additives are more vigorous in their attack on silver than others, and, consequently, such attack is more difiicult to minimize. However, the silver-protective agents are advantageously used, even with the more active selenium additives.

The agents of this invention may be used in lubricating oils containing, in addition to the selenium compounds, other additives such as polyvalent metal phenates (e. g., calcium cetyl phenate), metal organo-sulfonates (e. g., calcium petroleum sulfonate), polyvalent metal salts of acids of phosphorus, such as phosphates (e. g., calcium cetyl phosphate), phosphonates (e. g., calcium white oil phosphonate), thiophosphates (e. g., calcium cetyl thiophosphates), phenols (e. g., 2,6-di-tertiary-butyl-4-methylphenol), etc.

The lubricant compositions of this invention may also contain other agents which are advantageously present, such as oiliness agents, blooming agents, viscosity index improvers, pour point depressants, peptizing agents, etc.

For the purpose of the tests described hereinbelow, the silver protective agents of this invention were incorporated in a California solvent.

refined S. A. E. 30 parafiinic base oil containing calcium petroleum sulfonate, sulfurized calcium cetyl phenate and a didodecyl monoselenide.

Table I below presents data obtained in the "silver strip test.

Table II below presents the results obtained when freshly polished silver strips were immersed for 30 minutes at a temperature of 300 F. in a California solvent refined S. A. E. 30 paraffinic base oil containing calcium petroleum sulfonate, sulfurized calcium cetyl phenate and 0.2% by weight of various selenium compounds 6 with and. without 2 mercapto 4,6,6 trimethyl thiazine as'a silver protective agent. The darker the appearance of the silver strip, the more pronounced the attack on the silver by the selenium compound.

1 0.4% by weight of selenium compound present.

We claim:

1. A lubricant consisting essentially of a major portion of a selenium-containing lubricating oil composition corrosive to silver, and a small amount, sufficient substantially to inhibit the formation of silver selenide resulting from the selenium attack on silver, of a Z-mercapto-thiazine wherein not more than four of the ring carbons contain aliphatic groups each of which has not more than 4 carbon atoms.

2. A lubricant consisting essentially of a major portion of a selenium-containing lubricating oil composition which is corrosive to silver, and a 7 small amount, sufficient substantially to inhibit the reaction between the selenium of said lubrieating oil composition and silver, a Z-mercaptothiazine wherein not more than four of the ring carbons contain short chain aliphatic groups, said aliphatic groups containing a total of no more than 16 carbon atoms.

3. A lubricating oil composition at least of which is composed of an admixture of an oil of lubricating viscosity and lubricating oil additives having present selenium which reacts with silver-wearing surfaces, and a small amount, sufiicient substantially to inhibit the reaction between the selenium and silver, of a 2 -mercapto-thiazine wherein not more than four of the ring carbons of the said mercapto-thiazine contain short chain aliphatic carbons.

4. A lubricant consisting essentially of a major portion of a selenium-containing lubricating oil composition which attacks silver directly to form silver selenide, and a small amount, sumcient substantially to reduce the selenium attack on silver, of a Z-mercapto-thiazine wherein not more than 4 of the ring carbons contain shortchain aliphatic groups.

5. A lubricant consisting essentially of a major portion of a selenium-containing lubricating oil composition which attacks silver-wearing surfaces to form silver selenide, and a small amount, sufiicient substantially to reduce the selenium attack on silver, of a 2-mercapto-4,6,6-trimethyl thiazine.

6. A selenium-containing lubricating oil composition which forms silver selenide on silverwearing surfaces, and a small amount, sufiicient substantially to reduce this silver selenide formation, of a 2-mercapto-thiazine wherein not more than four of the ring carbons contain short chain.::;aliphatic groups.:= said. i aliphatic "groups .1 containingra total-. of: not more-than 16 carbon:

atoms.

'7. -A selenium-containing lubricating joil' com-- position which forms silver selenide on silver- 85' mation, .of ':2-mercapto- 4,6,firtrimethyl thiazine. 9. 'Alubricantcompositioncomprising a 'major' proportion of an oil of. lubricating wiscosity-,;-' a selenium -.compound which attacks silver -wear' ing surfacesto form: silver selenide, and a small-w amount; sufiicien-tsubstantially .1 to reduce the Y selenium attack on silver," 1 of" a r Z-mercaptothiazinawherein not moi-Ethan four ofthe ring -1- ca'rbons contain-short chain aliphatic groups.

WARREN LOW'E. W-I-LLIAM-- T; STEWARE: J AMES- 0. CLAYTON-.-

No references cited.- 

1. A LUBRICANT CONSISTING ESSENTIALLY OF A MAJOR PORTION OF A SELENIUM-CONTAINING LUBRICATING OIL COMPOSITION CORROSIVE TO SILVER, AND A SMALL AMOUNT, SUFFICIENT SUBSTANTIALLY TO INHIBIT THE FORMATION OF SILVER SELENIDE RESULTING FROM THE SELENIUM ATTACK ON SILVER, OF A 2-MERCAPTO-THIAZINE WHEREIN NOT MORE THAN FOUR OF THE RING CARBONS CONTAIN ALIPHATIC GROUPS EACH OF WHICH HAS NOT MORE THAN 4 CARBON ATOMS. 